1. Field of the Invention
The present invention relates to a hydrodynamic bearing assembly and a spindle motor having the same.
2. Description of the Related Art
A small spindle motor used in a hard disk drive (HDD) is generally provided with a dynamic pressure bearing apparatus, and a bearing clearance formed between a shaft and a sleeve included in the dynamic pressure bearing apparatus is filled with a lubricating fluid such as oil. The lubricating fluid provided in the bearing clearance as described above is pumped to generate fluid dynamic pressure, thereby rotatably supporting a rotating member.
That is, the dynamic pressure bearing apparatus is generally provided with a thrust dynamic pressure groove having a spiral shape or a journal dynamic pressure groove having a herringbone shape, both of which generate dynamic pressure to thereby promote stability in rotational driving of a motor.
Meanwhile, at the time of rotating the rotating member, the lubricating fluid is pumped while being introduced into the thrust dynamic pressure groove and the journal dynamic pressure groove as described above, thereby generating fluid dynamic pressure.
However, as described above, in the case that the lubricating fluid is introduced into the thrust dynamic pressure groove and the journal dynamic pressure groove, it is likely that an area of low pressure will be generated in a location at which the lubricating fluid is introduced. In addition, it is further likely that the area of low pressure will be generated in the location in which the lubricating fluid is introduced into the thrust dynamic pressure groove and the journal dynamic pressure groove disposed close to the surrounding air.
The area of low pressure generated as described above may cause cavitation (that is, a phenomenon in which cavities are formed within a liquid due to areas of low pressure therein), thereby deteriorating rotational characteristics.